The central retinal artery and vein, the vessels that can be seen and assessed with an ophthalmoscope, pass through the center of the optic nerve to enter the bulb of the eye at the optic disc (see Fig. 23.2 and pages 791 to 792, the section on the developing eye). The artery branches immediately into upper and lower branches, each of which divides again. Veins undergo a similar pattern of branching. The vessels initially lie between the vitreous body and inner limiting membrane. As the vessels pass laterally, they pass deeper within the inner retinal layers. Branches from these vessels form a capillary plexus that does not extend beyond the inner nuclear layer. The branches of the central retinal artery do not anastomose and therefore are classified as anatomic end arteries. Evaluation of the retinal vessels and optic disc during the physical examination of a patient not only provides important information on the state of the eye but also provides early clinical signs of a number of conditions, including elevated intracranial pressure, hypertension, glaucoma, and diabetes.
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